1. Field of Invention
This invention relates to a method for processing signals, and more particularly to a method for processing signals of a touch panel.
2. Related Art
Techniques of touch panels are advanced in recent years, such as resistive touch panels, capacitive touch panels, surface acoustic wave touch panels, and optical touch panels. The said techniques have been applied to communication products, computer devices and consumer electronic products for increasing functions of said applied products and convenient usage.
The capacitive touch panels can be operated by fingers without pressing the capacitive touch panels heavily, so the capacitive touch panels has no disadvantage of a stress caused by repeatedly touching the touch panel, and a damage caused by deformation. Advantages of the capacitive touch panels are that the capacitive touch panels are with simple structures, less elements and a high product yield rate, so the capacitive touch panels are adapted for mass production, whereby the cost of the capacitive touch panels can be reduced.
FIG. 1 shows a cross sectional view of a conventional touch sensor 100. The touch sensor 100 includes a glass substrate 110, two optically clear adhesive (OCA) layers 120, an indium tin oxide (ITO) layer 130 and a cover lens 140. A gap of the touch sensor 100 between the glass substrate 110 and the ITO layer 130 is filled with one of the two OCA layers 120 for bonding the glass substrate 110 and the ITO layer 130; the other gap of the touch sensor 100 between the ITO layer 130 and the cover lens 140 is filled with another OCA layer 120 for bonding the ITO layer 130 and the cover lens 140.
FIG. 2 is a cross sectional view of a conventional touch panel 200. The conventional touch panel 200 includes the touch sensor 100 and a liquid crystal display module (LCM) 250. The touch sensor 100 is located above the LCM 250. An air gap 260 is formed between the glass substrate 110 and the LCM 250.
FIG. 3 is a schematic view showing signal processing of the conventional touch panel. The conventional touch panel includes the touch sensor 100, an analog to digital (A/D) converter 330, a microcontroller 340, a transmission interface 350 and an operating system 360. When the touch panel 200 is touched, a corresponding capacitance value is changed. Then, the touch sensor 100 outputs an analog signal to the A/D converter 330. The A/D converter 330 converts the analog signal to a digital signal, and then outputs the digital signal to the microcontroller 340. The microcontroller 340 processes the digital signal, and then outputs a control signal. Finally, the control signal is transmitted to an operating system 360 through the transmission interface 350 for determining touch locations of the touch panel 200.
However, after a touch sensor is assembled on an LCD module, the touch sensor is interfered by noises generated from the LCD module so as to cause a misjudgment of touch locations. For example, when the LCD module is normally operated, different surface noises are generated by different pictures of the LCD module. For another example, when the picture of the LCD module is fast updated or is in a heavy loading, an unstable voltage (i.e. surface noise) is detected from a surface of the LCD module. FIG. 4 is timing charts of the surface noises of the LCD module. When red, green and blue (RGB) pixels of the LCD module show a picture having bright lines and dark lines separated from one another, or the RGB pixels of the LCD module show a black picture (heavy loading), the surface noises can be generated.
Accordingly, a problem of the surface noises for the touch panel and a method for processing signal of the touch panel needs to be solved.